RUA: hand off RANAP from all PDU types, not just UnitDataTransfer

Also, we now offer a ranap_tx_dt() message for connection-oriented
RANAP transfers.  A far as I understand the RUA spec, on RUA layer,
all operations are Class 2, i.e. without any response/confirmation.
diff --git a/src/hnbgw_rua.h b/src/hnbgw_rua.h
index 69b2382..55acaf2 100644
--- a/src/hnbgw_rua.h
+++ b/src/hnbgw_rua.h
@@ -6,3 +6,4 @@
 int hnbgw_rua_init(void);
 
 int rua_tx_udt(struct msgb *inmsg);
+int rua_tx_dt(struct msgb *inmsg);